Our goal is to determine whether analysis of oscillatory patterns in respiration and heart rate can identify infants at risk to die of the Sudden Infant Death Syndrome, SIDS. Because oscillatory patterns underlie apnea and hypoventilatory events, analysis of these patterns, rather than tabulation of numbers of apneas or percent time apneic, may identify abnormalities associated with SIDS. Periodic breathing, sometimes used as a risk factor, is only one form of ventilatory oscillation. Our analysis covers a wide range of oscillatory phenomena and we determine many characteristics of the patterns, in addition to how often they are present. Data from SIDS victims and matched controls will be provided by Dr. David Southall, Cardiothoracic Institute, London, and will be drawn from his prospective recordings of respiration and heart rate on 9,251 infants, 29 of whom died of SIDS. In these 24-hour recordings, the respiration signal, from a pressure capsule taped to the abdomen, is similar to pneumogram recordings obtained from electrical impedance of the chest wall. Although inaccurate as a measure of mean ventilation, preliminary studies indicate that this type of recording can accurately convey oscillatory patterns in ventilation, particularly strong, low frequency patterns such as those expected to be correlated with high risk for SIDS. The presence of mixed and obstructive apneas cannot be determined from these recordings. However, oscillatory patterns which accompany such apneas can still be identified. Assessment of normal versus abnormal characteristics will be based on whether apneas are related to breathing patterns as opposed to being idiopathic, whether the apneas which are related to breathing patterns are of an appropriate duration, whether pattern characteristics including the incidence, cycle time, and strength of the patterns, are normal, and whether patterns in heart rate are associated with patterns in respiration, with emphasis on the phase and amplitude relationships between these patterns. Abnormality in any or all of these areas may be indicative of increased risk for SIDS. Identification of risk for SIDS is important both as a step toward understanding the cause of SIDS and so that prophylaxis can be attempted on the "at risk" population.